Steenbras groundwater extracted
HELDERBERG – The first groundwater supply project of the Table Mountain Group (TMG) Aquifer at the Steenbras Dam is now operational.
From the first phase of the project, an additional 30 million litres of water daily will be contributed to the City of Cape Town’s water system once the project is fully completed. The project was launched by mayor Dan Plato and Xanthea Limberg, Mayoral Committee member for Warer and Waste, last Wednesday (5 August).
The milestone achievement in the implementation of the Cape Town Water Strategy addresses water supply security and other aspects of our shared water future as groundwater is a key part of the City’s new water supply programme, in a bid to diversify the mix of water sources available.
Council initiated drilling operations at Steenbras during the drought crisis and the TMG Aquifer is now producing its first yield of groundwater at the Steenbras Wellfield. It is believed to be the largest in the world, with drilling reaching a depth of 710 m below ground.
“The launch of the first groundwater from the TMG Aquifer is very exciting because this is testament to the City’s commitment to contributing to our long-term water security,” explained Plato. “This milestone needs to be celebrated as it is a step closer to seeing our water strategy become a reality. The TMG Aquifer is one of the projects listed in the strategy, which was launched in February.”
The strategy aims to make Cape Town more resilient to drought and other climate shocks, and takes into account the relationships among water, people, the economy and the environment, he added.
The TMG Aquifer is a geological formation that extends from Nieuwoudtville to Cape Agulhas and Port Elizabeth. It is identified as a significant source of groundwater storage in the Western Cape. There are currently eight completed production boreholes, yielding almost 20 million litres per day.
Drilling of a further four is underway, which will eventually increase the yield to 30 million litres per day.
“To put this into context, 30 million litres per day is the equivalent of a daily water supply for around 200 000 people at current consumption levels of 125 litres of water per person, per day,” Limberg related.
“Alternatively, this would represent 16 days’ worth of water for the whole city, for every year of operation. Although there isn’t currently an urgent threat to our immediate water security – provided current restrictions are adhered to – we are still encouraging residents not to forget the very valuable lessons learnt about the finite nature of water, our most precious resource.”
The Steenbras Wellfield was chosen due to favourable hydrogeological conditions giving rise to a potentially high groundwater yield, Limberg explained, with the benefit of it being in close proximity to the Steenbras Dam. “This is ideal as the groundwater can be pumped directly into the dam and treated at the Faure water treatment works to drinking-water standard.”
A key highlight in this project is the environmental mitigation and controls administered to ensure the protection of the Steenbras Nature Reserve, which falls within the Kogelberg Biosphere Reserve.
These measures include the search and rescue of protected vegetation, top soil management, re-using on-site material to prevent changes to ground conditions, matching historical groundwater and surface water movement across trenches, installing power lines underground to allow for veld fire preventative management and reducing the visual impact of pylons, spanning pipelines across rivers instead of trenching through them as well as rehabilitating disturbed areas after construction.
Due to the environmental sensitivity of the area and the risk of damage by natural fire cycles in fynbos, medium-voltage power cables and fiberoptic cables were buried in the same trenches as the pipelines.
The fiberoptic cable network feeds all data from the respective bore-holes to a centralised Supervisory Control and Data Acquisition point (Scada), which allows the wellfield to be controlled and operated through an automated system.
“Invasive alien vegetation is being removed from the reserve’s catchment area, in an effort to maximise the rainwater surface run-off yield into the dam,” Limberg related. “Pine and bluegum trees are being systematically removed and the land is carefully rehabilitated with indigenous vegetation.
Alien vegetation clearance and other short-term projects, are also providing local work opportunities through the Expanded Public Works Programme.”
The national departments of Human Settlements and Water and Sanitation is the custodian of groundwater in SA, and has issued the City with a water-use licence to extract water and construct infrastructure for the project. Total licensed volume for Phase 1 of the project is 33 million litres per day, with an additional 15 million expected from the Nuweberg Wellfield, now in exploratory drilling phase. So the Steenbras Wellfield forms part of the Western Cape Water Supply System, and was established in collaboration with the national Department of
Water and Sanitation.